/ Check-in [98853f61]
Login

Many hyperlinks are disabled.
Use anonymous login to enable hyperlinks.

Overview
Comment:Generalize the IS and IS NOT operators so that their right-hand side can be an arbitrary expression and not simple the constant NULL. They work like = and <> except that NULL values compare equal to one another an unequal to everything else.
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1:98853f6104076c50ea92175e17a3254bfbbd4619
User & Date: drh 2009-09-23 02:29:37
References
2014-10-02
21:25 New ticket [8c32a33a] Segfault on a syntax error involving the IS operator. artifact: 7de8fdb3 user: drh
Context
2009-09-23
03:01
Do not run ON UPDATE actions of a foreign key constraint unless at least one column value really does change. check-in: 71ac8e28 user: drh tags: trunk
02:29
Generalize the IS and IS NOT operators so that their right-hand side can be an arbitrary expression and not simple the constant NULL. They work like = and <> except that NULL values compare equal to one another an unequal to everything else. check-in: 98853f61 user: drh tags: trunk
2009-09-22
20:08
Factor the UMINUS and UPLUS tokens out of the parser so that the parser tables can go back to using 8-bit values instead of 16-bit values. check-in: 3fc938c9 user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to addopcodes.awk.

15
16
17
18
19
20
21

22
23
24
25
26
27
28
29
30
31
32
33
}
END {
  printf "#define TK_%-29s %4d\n", "TO_TEXT",         ++max
  printf "#define TK_%-29s %4d\n", "TO_BLOB",         ++max
  printf "#define TK_%-29s %4d\n", "TO_NUMERIC",      ++max
  printf "#define TK_%-29s %4d\n", "TO_INT",          ++max
  printf "#define TK_%-29s %4d\n", "TO_REAL",         ++max

  printf "#define TK_%-29s %4d\n", "END_OF_FILE",     ++max
  printf "#define TK_%-29s %4d\n", "ILLEGAL",         ++max
  printf "#define TK_%-29s %4d\n", "SPACE",           ++max
  printf "#define TK_%-29s %4d\n", "UNCLOSED_STRING", ++max
  printf "#define TK_%-29s %4d\n", "FUNCTION",        ++max
  printf "#define TK_%-29s %4d\n", "COLUMN",          ++max
  printf "#define TK_%-29s %4d\n", "AGG_FUNCTION",    ++max
  printf "#define TK_%-29s %4d\n", "AGG_COLUMN",      ++max
  printf "#define TK_%-29s %4d\n", "CONST_FUNC",      ++max
  printf "#define TK_%-29s %4d\n", "UMINUS",          ++max
  printf "#define TK_%-29s %4d\n", "UPLUS",           ++max
}







>












15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
}
END {
  printf "#define TK_%-29s %4d\n", "TO_TEXT",         ++max
  printf "#define TK_%-29s %4d\n", "TO_BLOB",         ++max
  printf "#define TK_%-29s %4d\n", "TO_NUMERIC",      ++max
  printf "#define TK_%-29s %4d\n", "TO_INT",          ++max
  printf "#define TK_%-29s %4d\n", "TO_REAL",         ++max
  printf "#define TK_%-29s %4d\n", "ISNOT",           ++max
  printf "#define TK_%-29s %4d\n", "END_OF_FILE",     ++max
  printf "#define TK_%-29s %4d\n", "ILLEGAL",         ++max
  printf "#define TK_%-29s %4d\n", "SPACE",           ++max
  printf "#define TK_%-29s %4d\n", "UNCLOSED_STRING", ++max
  printf "#define TK_%-29s %4d\n", "FUNCTION",        ++max
  printf "#define TK_%-29s %4d\n", "COLUMN",          ++max
  printf "#define TK_%-29s %4d\n", "AGG_FUNCTION",    ++max
  printf "#define TK_%-29s %4d\n", "AGG_COLUMN",      ++max
  printf "#define TK_%-29s %4d\n", "CONST_FUNC",      ++max
  printf "#define TK_%-29s %4d\n", "UMINUS",          ++max
  printf "#define TK_%-29s %4d\n", "UPLUS",           ++max
}

Changes to src/expr.c.

148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
....
2239
2240
2241
2242
2243
2244
2245













2246
2247
2248
2249
2250
2251
2252
....
3013
3014
3015
3016
3017
3018
3019













3020
3021
3022
3023
3024
3025
3026
....
3162
3163
3164
3165
3166
3167
3168













3169
3170
3171
3172
3173
3174
3175
** pExpr is a comparison operator.  Return the type affinity that should
** be applied to both operands prior to doing the comparison.
*/
static char comparisonAffinity(Expr *pExpr){
  char aff;
  assert( pExpr->op==TK_EQ || pExpr->op==TK_IN || pExpr->op==TK_LT ||
          pExpr->op==TK_GT || pExpr->op==TK_GE || pExpr->op==TK_LE ||
          pExpr->op==TK_NE );
  assert( pExpr->pLeft );
  aff = sqlite3ExprAffinity(pExpr->pLeft);
  if( pExpr->pRight ){
    aff = sqlite3CompareAffinity(pExpr->pRight, aff);
  }else if( ExprHasProperty(pExpr, EP_xIsSelect) ){
    aff = sqlite3CompareAffinity(pExpr->x.pSelect->pEList->a[0].pExpr, aff);
  }else if( !aff ){
................................................................................
      codeCompareOperands(pParse, pExpr->pLeft, &r1, &regFree1,
                                  pExpr->pRight, &r2, &regFree2);
      codeCompare(pParse, pExpr->pLeft, pExpr->pRight, op,
                  r1, r2, inReg, SQLITE_STOREP2);
      testcase( regFree1==0 );
      testcase( regFree2==0 );
      break;













    }
    case TK_AND:
    case TK_OR:
    case TK_PLUS:
    case TK_STAR:
    case TK_MINUS:
    case TK_REM:
................................................................................
      codeCompareOperands(pParse, pExpr->pLeft, &r1, &regFree1,
                                  pExpr->pRight, &r2, &regFree2);
      codeCompare(pParse, pExpr->pLeft, pExpr->pRight, op,
                  r1, r2, dest, jumpIfNull);
      testcase( regFree1==0 );
      testcase( regFree2==0 );
      break;













    }
    case TK_ISNULL:
    case TK_NOTNULL: {
      assert( TK_ISNULL==OP_IsNull );
      assert( TK_NOTNULL==OP_NotNull );
      testcase( op==TK_ISNULL );
      testcase( op==TK_NOTNULL );
................................................................................
      codeCompareOperands(pParse, pExpr->pLeft, &r1, &regFree1,
                                  pExpr->pRight, &r2, &regFree2);
      codeCompare(pParse, pExpr->pLeft, pExpr->pRight, op,
                  r1, r2, dest, jumpIfNull);
      testcase( regFree1==0 );
      testcase( regFree2==0 );
      break;













    }
    case TK_ISNULL:
    case TK_NOTNULL: {
      testcase( op==TK_ISNULL );
      testcase( op==TK_NOTNULL );
      r1 = sqlite3ExprCodeTemp(pParse, pExpr->pLeft, &regFree1);
      sqlite3VdbeAddOp2(v, op, r1, dest);







|







 







>
>
>
>
>
>
>
>
>
>
>
>
>







 







>
>
>
>
>
>
>
>
>
>
>
>
>







 







>
>
>
>
>
>
>
>
>
>
>
>
>







148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
....
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
....
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
....
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
** pExpr is a comparison operator.  Return the type affinity that should
** be applied to both operands prior to doing the comparison.
*/
static char comparisonAffinity(Expr *pExpr){
  char aff;
  assert( pExpr->op==TK_EQ || pExpr->op==TK_IN || pExpr->op==TK_LT ||
          pExpr->op==TK_GT || pExpr->op==TK_GE || pExpr->op==TK_LE ||
          pExpr->op==TK_NE || pExpr->op==TK_IS || pExpr->op==TK_ISNOT );
  assert( pExpr->pLeft );
  aff = sqlite3ExprAffinity(pExpr->pLeft);
  if( pExpr->pRight ){
    aff = sqlite3CompareAffinity(pExpr->pRight, aff);
  }else if( ExprHasProperty(pExpr, EP_xIsSelect) ){
    aff = sqlite3CompareAffinity(pExpr->x.pSelect->pEList->a[0].pExpr, aff);
  }else if( !aff ){
................................................................................
      codeCompareOperands(pParse, pExpr->pLeft, &r1, &regFree1,
                                  pExpr->pRight, &r2, &regFree2);
      codeCompare(pParse, pExpr->pLeft, pExpr->pRight, op,
                  r1, r2, inReg, SQLITE_STOREP2);
      testcase( regFree1==0 );
      testcase( regFree2==0 );
      break;
    }
    case TK_IS:
    case TK_ISNOT: {
      testcase( op==TK_IS );
      testcase( op==TK_ISNOT );
      codeCompareOperands(pParse, pExpr->pLeft, &r1, &regFree1,
                                  pExpr->pRight, &r2, &regFree2);
      op = (op==TK_IS) ? TK_EQ : TK_NE;
      codeCompare(pParse, pExpr->pLeft, pExpr->pRight, op,
                  r1, r2, inReg, SQLITE_STOREP2 | SQLITE_NULLEQ);
      testcase( regFree1==0 );
      testcase( regFree2==0 );
      break;
    }
    case TK_AND:
    case TK_OR:
    case TK_PLUS:
    case TK_STAR:
    case TK_MINUS:
    case TK_REM:
................................................................................
      codeCompareOperands(pParse, pExpr->pLeft, &r1, &regFree1,
                                  pExpr->pRight, &r2, &regFree2);
      codeCompare(pParse, pExpr->pLeft, pExpr->pRight, op,
                  r1, r2, dest, jumpIfNull);
      testcase( regFree1==0 );
      testcase( regFree2==0 );
      break;
    }
    case TK_IS:
    case TK_ISNOT: {
      testcase( op==TK_IS );
      testcase( op==TK_ISNOT );
      codeCompareOperands(pParse, pExpr->pLeft, &r1, &regFree1,
                                  pExpr->pRight, &r2, &regFree2);
      op = (op==TK_IS) ? TK_EQ : TK_NE;
      codeCompare(pParse, pExpr->pLeft, pExpr->pRight, op,
                  r1, r2, dest, SQLITE_NULLEQ);
      testcase( regFree1==0 );
      testcase( regFree2==0 );
      break;
    }
    case TK_ISNULL:
    case TK_NOTNULL: {
      assert( TK_ISNULL==OP_IsNull );
      assert( TK_NOTNULL==OP_NotNull );
      testcase( op==TK_ISNULL );
      testcase( op==TK_NOTNULL );
................................................................................
      codeCompareOperands(pParse, pExpr->pLeft, &r1, &regFree1,
                                  pExpr->pRight, &r2, &regFree2);
      codeCompare(pParse, pExpr->pLeft, pExpr->pRight, op,
                  r1, r2, dest, jumpIfNull);
      testcase( regFree1==0 );
      testcase( regFree2==0 );
      break;
    }
    case TK_IS:
    case TK_ISNOT: {
      testcase( op==TK_IS );
      testcase( op==TK_ISNOT );
      codeCompareOperands(pParse, pExpr->pLeft, &r1, &regFree1,
                                  pExpr->pRight, &r2, &regFree2);
      op = (pExpr->op==TK_IS) ? TK_NE : TK_EQ;
      codeCompare(pParse, pExpr->pLeft, pExpr->pRight, op,
                  r1, r2, dest, SQLITE_NULLEQ);
      testcase( regFree1==0 );
      testcase( regFree2==0 );
      break;
    }
    case TK_ISNULL:
    case TK_NOTNULL: {
      testcase( op==TK_ISNULL );
      testcase( op==TK_NOTNULL );
      r1 = sqlite3ExprCodeTemp(pParse, pExpr->pLeft, &regFree1);
      sqlite3VdbeAddOp2(v, op, r1, dest);

Changes to src/parse.y.

880
881
882
883
884
885
886
887
888













889
890





891
892
893
894
895
896
897
    pOut->pExpr = sqlite3PExpr(pParse, op, pOperand->pExpr, 0, 0);
    pOut->zStart = pOperand->zStart;
    pOut->zEnd = &pPostOp->z[pPostOp->n];
  }                           
}

expr(A) ::= expr(X) ISNULL|NOTNULL(E).   {spanUnaryPostfix(&A,pParse,@E,&X,&E);}
expr(A) ::= expr(X) IS NULL(E).   {spanUnaryPostfix(&A,pParse,TK_ISNULL,&X,&E);}
expr(A) ::= expr(X) NOT NULL(E). {spanUnaryPostfix(&A,pParse,TK_NOTNULL,&X,&E);}













expr(A) ::= expr(X) IS NOT NULL(E).
                                 {spanUnaryPostfix(&A,pParse,TK_NOTNULL,&X,&E);}






%include {
  /* Construct an expression node for a unary prefix operator
  */
  static void spanUnaryPrefix(
    ExprSpan *pOut,        /* Write the new expression node here */
    Parse *pParse,         /* Parsing context to record errors */







<

>
>
>
>
>
>
>
>
>
>
>
>
>
|
<
>
>
>
>
>







880
881
882
883
884
885
886

887
888
889
890
891
892
893
894
895
896
897
898
899
900
901

902
903
904
905
906
907
908
909
910
911
912
913
    pOut->pExpr = sqlite3PExpr(pParse, op, pOperand->pExpr, 0, 0);
    pOut->zStart = pOperand->zStart;
    pOut->zEnd = &pPostOp->z[pPostOp->n];
  }                           
}

expr(A) ::= expr(X) ISNULL|NOTNULL(E).   {spanUnaryPostfix(&A,pParse,@E,&X,&E);}

expr(A) ::= expr(X) NOT NULL(E). {spanUnaryPostfix(&A,pParse,TK_NOTNULL,&X,&E);}

//    expr1 IS expr2
//    expr1 IS NOT expr2
//
// If expr2 is NULL then code as TK_ISNULL or TK_NOTNULL.  If expr2
// is any other expression, code as TK_IS or TK_ISNOT.
// 
expr(A) ::= expr(X) IS expr(Y).     {
  spanBinaryExpr(&A,pParse,TK_IS,&X,&Y);
  if( pParse->db->mallocFailed==0  && Y.pExpr->op==TK_NULL ){
    A.pExpr->op = TK_ISNULL;
  }
}
expr(A) ::= expr(X) IS NOT expr(Y). {

  spanBinaryExpr(&A,pParse,TK_ISNOT,&X,&Y);
  if( pParse->db->mallocFailed==0  && Y.pExpr->op==TK_NULL ){
    A.pExpr->op = TK_NOTNULL;
  }
}

%include {
  /* Construct an expression node for a unary prefix operator
  */
  static void spanUnaryPrefix(
    ExprSpan *pOut,        /* Write the new expression node here */
    Parse *pParse,         /* Parsing context to record errors */

Changes to src/sqliteInt.h.

1122
1123
1124
1125
1126
1127
1128

1129
1130
1131
1132
1133
1134
1135

/*
** Additional bit values that can be ORed with an affinity without
** changing the affinity.
*/
#define SQLITE_JUMPIFNULL   0x08  /* jumps if either operand is NULL */
#define SQLITE_STOREP2      0x10  /* Store result in reg[P2] rather than jump */


/*
** An object of this type is created for each virtual table present in
** the database schema. 
**
** If the database schema is shared, then there is one instance of this
** structure for each database connection (sqlite3*) that uses the shared







>







1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136

/*
** Additional bit values that can be ORed with an affinity without
** changing the affinity.
*/
#define SQLITE_JUMPIFNULL   0x08  /* jumps if either operand is NULL */
#define SQLITE_STOREP2      0x10  /* Store result in reg[P2] rather than jump */
#define SQLITE_NULLEQ       0x80  /* NULL=NULL */

/*
** An object of this type is created for each virtual table present in
** the database schema. 
**
** If the database schema is shared, then there is one instance of this
** structure for each database connection (sqlite3*) that uses the shared

Changes to src/vdbe.c.

1676
1677
1678
1679
1680
1681
1682






1683
1684
1685
1686
1687
1688






1689
1690
1691
1692
1693
1694
1695
....
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720










1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733


1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744

1745
1746
1747
1748
1749
1750
1751
....
1803
1804
1805
1806
1807
1808
1809
1810
1811








1812


1813
1814
1815
1816
1817
1818
1819
** store a boolean result (either 0, or 1, or NULL) in register P2.
*/
/* Opcode: Ne P1 P2 P3 P4 P5
**
** This works just like the Lt opcode except that the jump is taken if
** the operands in registers P1 and P3 are not equal.  See the Lt opcode for
** additional information.






*/
/* Opcode: Eq P1 P2 P3 P4 P5
**
** This works just like the Lt opcode except that the jump is taken if
** the operands in registers P1 and P3 are equal.
** See the Lt opcode for additional information.






*/
/* Opcode: Le P1 P2 P3 P4 P5
**
** This works just like the Lt opcode except that the jump is taken if
** the content of register P3 is less than or equal to the content of
** register P1.  See the Lt opcode for additional information.
*/
................................................................................
*/
case OP_Eq:               /* same as TK_EQ, jump, in1, in3 */
case OP_Ne:               /* same as TK_NE, jump, in1, in3 */
case OP_Lt:               /* same as TK_LT, jump, in1, in3 */
case OP_Le:               /* same as TK_LE, jump, in1, in3 */
case OP_Gt:               /* same as TK_GT, jump, in1, in3 */
case OP_Ge: {             /* same as TK_GE, jump, in1, in3 */
  int flags;
  int res;
  char affinity;

  flags = pIn1->flags|pIn3->flags;

  if( flags&MEM_Null ){










    /* If either operand is NULL then the result is always NULL.
    ** The jump is taken if the SQLITE_JUMPIFNULL bit is set.
    */
    if( pOp->p5 & SQLITE_STOREP2 ){
      pOut = &p->aMem[pOp->p2];
      MemSetTypeFlag(pOut, MEM_Null);
      REGISTER_TRACE(pOp->p2, pOut);
    }else if( pOp->p5 & SQLITE_JUMPIFNULL ){
      pc = pOp->p2-1;
    }
    break;
  }



  affinity = pOp->p5 & SQLITE_AFF_MASK;
  if( affinity ){
    applyAffinity(pIn1, affinity, encoding);
    applyAffinity(pIn3, affinity, encoding);
    if( db->mallocFailed ) goto no_mem;
  }

  assert( pOp->p4type==P4_COLLSEQ || pOp->p4.pColl==0 );
  ExpandBlob(pIn1);
  ExpandBlob(pIn3);
  res = sqlite3MemCompare(pIn3, pIn1, pOp->p4.pColl);

  switch( pOp->opcode ){
    case OP_Eq:    res = res==0;     break;
    case OP_Ne:    res = res!=0;     break;
    case OP_Lt:    res = res<0;      break;
    case OP_Le:    res = res<=0;     break;
    case OP_Gt:    res = res>0;      break;
    default:       res = res>=0;     break;
................................................................................
  int bRev;          /* True for DESCENDING sort order */

  n = pOp->p3;
  pKeyInfo = pOp->p4.pKeyInfo;
  assert( n>0 );
  assert( pKeyInfo!=0 );
  p1 = pOp->p1;
  assert( p1>0 && p1+n<=p->nMem+1 );
  p2 = pOp->p2;








  assert( p2>0 && p2+n<=p->nMem+1 );


  for(i=0; i<n; i++){
    idx = aPermute ? aPermute[i] : i;
    REGISTER_TRACE(p1+idx, &p->aMem[p1+idx]);
    REGISTER_TRACE(p2+idx, &p->aMem[p2+idx]);
    assert( i<pKeyInfo->nField );
    pColl = pKeyInfo->aColl[i];
    bRev = pKeyInfo->aSortOrder[i];







>
>
>
>
>
>






>
>
>
>
>
>







 







|
<
|

<
<
|
>
>
>
>
>
>
>
>
>
>
|
|
|
|
|
|
|
|
|
|
|
|
<
>
>
|
|
|
|
|
|

|
|
|
|
>







 







<

>
>
>
>
>
>
>
>
|
>
>







1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
....
1719
1720
1721
1722
1723
1724
1725
1726

1727
1728


1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751

1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
....
1824
1825
1826
1827
1828
1829
1830

1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
** store a boolean result (either 0, or 1, or NULL) in register P2.
*/
/* Opcode: Ne P1 P2 P3 P4 P5
**
** This works just like the Lt opcode except that the jump is taken if
** the operands in registers P1 and P3 are not equal.  See the Lt opcode for
** additional information.
**
** If SQLITE_NULLEQ is set in P5 then the result of comparison is always either
** true or false and is never NULL.  If both operands are NULL then the result
** of comparison is false.  If either operand is NULL then the result is true.
** If neither operand is NULL the the result is the same as it would be if
** the SQLITE_NULLEQ flag were omitted from P5.
*/
/* Opcode: Eq P1 P2 P3 P4 P5
**
** This works just like the Lt opcode except that the jump is taken if
** the operands in registers P1 and P3 are equal.
** See the Lt opcode for additional information.
**
** If SQLITE_NULLEQ is set in P5 then the result of comparison is always either
** true or false and is never NULL.  If both operands are NULL then the result
** of comparison is true.  If either operand is NULL then the result is false.
** If neither operand is NULL the the result is the same as it would be if
** the SQLITE_NULLEQ flag were omitted from P5.
*/
/* Opcode: Le P1 P2 P3 P4 P5
**
** This works just like the Lt opcode except that the jump is taken if
** the content of register P3 is less than or equal to the content of
** register P1.  See the Lt opcode for additional information.
*/
................................................................................
*/
case OP_Eq:               /* same as TK_EQ, jump, in1, in3 */
case OP_Ne:               /* same as TK_NE, jump, in1, in3 */
case OP_Lt:               /* same as TK_LT, jump, in1, in3 */
case OP_Le:               /* same as TK_LE, jump, in1, in3 */
case OP_Gt:               /* same as TK_GT, jump, in1, in3 */
case OP_Ge: {             /* same as TK_GE, jump, in1, in3 */
  int res;            /* Result of the comparison of pIn1 against pIn3 */

  char affinity;      /* Affinity to use for comparison */



  if( (pIn1->flags | pIn3->flags)&MEM_Null ){
    /* One or both operands are NULL */
    if( pOp->p5 & SQLITE_NULLEQ ){
      /* If SQLITE_NULLEQ is set (which will only happen if the operator is
      ** OP_Eq or OP_Ne) then take the jump or not depending on whether
      ** or not both operands are null.
      */
      assert( pOp->opcode==OP_Eq || pOp->opcode==OP_Ne );
      res = (pIn1->flags & pIn3->flags & MEM_Null)==0;
    }else{
      /* SQLITE_NULLEQ is clear and at least one operand is NULL,
      ** then the result is always NULL.
      ** The jump is taken if the SQLITE_JUMPIFNULL bit is set.
      */
      if( pOp->p5 & SQLITE_STOREP2 ){
        pOut = &p->aMem[pOp->p2];
        MemSetTypeFlag(pOut, MEM_Null);
        REGISTER_TRACE(pOp->p2, pOut);
      }else if( pOp->p5 & SQLITE_JUMPIFNULL ){
        pc = pOp->p2-1;
      }
      break;
    }

  }else{
    /* Neither operand is NULL.  Do a comparison. */
    affinity = pOp->p5 & SQLITE_AFF_MASK;
    if( affinity ){
      applyAffinity(pIn1, affinity, encoding);
      applyAffinity(pIn3, affinity, encoding);
      if( db->mallocFailed ) goto no_mem;
    }

    assert( pOp->p4type==P4_COLLSEQ || pOp->p4.pColl==0 );
    ExpandBlob(pIn1);
    ExpandBlob(pIn3);
    res = sqlite3MemCompare(pIn3, pIn1, pOp->p4.pColl);
  }
  switch( pOp->opcode ){
    case OP_Eq:    res = res==0;     break;
    case OP_Ne:    res = res!=0;     break;
    case OP_Lt:    res = res<0;      break;
    case OP_Le:    res = res<=0;     break;
    case OP_Gt:    res = res>0;      break;
    default:       res = res>=0;     break;
................................................................................
  int bRev;          /* True for DESCENDING sort order */

  n = pOp->p3;
  pKeyInfo = pOp->p4.pKeyInfo;
  assert( n>0 );
  assert( pKeyInfo!=0 );
  p1 = pOp->p1;

  p2 = pOp->p2;
#if SQLITE_DEBUG
  if( aPermute ){
    int k, mx = 0;
    for(k=0; k<n; k++) if( aPermute[k]>mx ) mx = aPermute[k];
    assert( p1>0 && p1+mx<=p->nMem+1 );
    assert( p2>0 && p2+mx<=p->nMem+1 );
  }else{
    assert( p1>0 && p1+n<=p->nMem+1 );
    assert( p2>0 && p2+n<=p->nMem+1 );
  }
#endif /* SQLITE_DEBUG */
  for(i=0; i<n; i++){
    idx = aPermute ? aPermute[i] : i;
    REGISTER_TRACE(p1+idx, &p->aMem[p1+idx]);
    REGISTER_TRACE(p2+idx, &p->aMem[p2+idx]);
    assert( i<pKeyInfo->nField );
    pColl = pKeyInfo->aColl[i];
    bRev = pKeyInfo->aSortOrder[i];